<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  <button>按钮1</button>
  <button>按钮2</button>
  <button>按钮3</button>
  <script>
     // window 是浏览器对象
     console.log(window);
      // document 是文档对象（当前文件）
      console.log(document);

      // 修改文档标题
      document.title = "文档标题被修改了";

      // 访问文档的 body
      console.log(document.body);

    const btn=document.querySelector('button');
    console.log(btn);
    const butns=document.querySelectorAll('button');
    console.log(butns);
    
  </script>
</body>
</html>